Conventionally, there is known a process for producing chlorine dioxide gas through an electrolysis reaction of an electrolytic solution containing chlorite (Patent Document 1).
It is well-known that there occurs change over time in the acid-base properties (pH) on the cathode side in the case of generating a gas on the anode side through an electrolysis reaction of an electrolytic solution. And, there is a concern that such change in the acid-base properties adversely affects the electrolytic solution present around the anode, leading to decrease in the stability of the electrolytic solution and progressive deterioration in the gas generation efficiency.
Patent Document 2 discloses a chlorine dioxide producing process in which a direct current is supplied to electrolytic solution inside a non-diaphragm electrolyzer tank having an anode and a cathode thereby to effect an electrolysis reaction for generating chlorine dioxide. More particularly, according to this process, the electrolysis reaction is carried out by supplying direct current to the electrolytic solution containing alkali chloride, alkaline chlorite, and a pH regulating agent, with the pH of the electrolytic solution being set from 4 to 8. In the course of the electrolysis reaction, in order to compensate for an amount of alkaline chlorite consumed in association with the electrolysis reaction, an amount of aqueous solution with alkaline chlorite is supplied to the electrolytic solution from the outside of the electrolyzer tank, and generated chlorine dioxide is extracted from the electrolytic solution. Thus, this process is configured as a single-liquid electrolysis type chlorine dioxide producing process.